1. Field of the Invention
The invention relates generally to wireless communication systems and, more particularly, to digital data transfer in a wireless communication system.
2. Description of the Related Art
Digital data communication systems are becoming more and more pervasive. For example, the Internet is commonly used to transfer digital data in the form of e-mail messages, web pages as well as audio, graphic and video information in digital format between many users and servers. FIG. 1 is a block diagram showing a typical Internet digital data system. The Internet “cloud” 10 interconnects a large number of users and content servers. In order to gain access to the Internet cloud 10, an Internet service provider 12 acts as a gateway between the Internet cloud 10 and a group of users 14A-14N.
In the normal course of “surfing the web”, a user accesses a series of web pages stored within a variety of content servers 8A-8N coupled to the Internet cloud 10. In general, a user requests a web page via browser software. The browser software retrieves the web page using a group of protocols defining the Internet. For example, the browser software uses the HyperText Transfer Protocol (HTTP) on top of Transmission Control Protocol/Internet Protocol (TCP/IP) to retrieve the web page. During the retrieval process, the user must wait as the browser software first makes a request for a Domain Name System (DNS) to find the appropriate content server, and then individually requests and receives the set of objects that make up the web page.
Each HTTP request to the content server opens a new TCP connection. After the connection is established, the user's browser software sends the HTTP request for the specific hypertext markup language (HTML) object. The wait experienced by the user is caused by the round-trip delay from the HTTP latency as all the HTML objects which compose the hypertext markup language (HTML) file are retrieved from the Internet.
The content server can be located many thousands of miles away from the user. Over such great distances, even if the messages were able to travel the speed of light, a significant latency would be accumulated by the numerous round-trip delays associated with retrieving each object.
The HTML file is digital data file that provides information to the browser such as display information. Generally, the HTML file comprises a set of embedded HTML objects. For example, the embedded objects may include Java applets, JPEG or GIF graphical objects, video files or sound clips. For example, a typical web page, such as the YAHOO!® home page, is an HTML file which designates many embedded objects such as advertisement banners, headline banners, the YAHOO!® logo and linking soft buttons. As an entire web page is retrieved, the browsers used by the users 14A-14N individually request each of the embedded objects. Thus, the response time associated with creating a fully displayed web page includes the time required to retrieve both the HTML file and all of the embedded objects referenced therein.
In order to decrease the waiting time of the system as well as decrease the amount of data that is transferred between the Internet 10 and the Internet service provider 12 of FIG. 1, the Internet service provider 12 may incorporate a cache 16. Generally, the cache 16 may be embodied as a fast storage buffer or memory that can be accessed by a central processing unit within the Internet service provider 12. The cache 16 can be used to store HTML objects and other files such as graphic files or sound clips that are commonly requested by the users 14A-14N. For example, the YAHOO!® home page HTML file is likely to be accessed by a large number of the users 14A-14N on a daily basis. Therefore, in order to avoid downloading the YAHOO!® HTML file with its many HTML embedded objects multiple times during the day, the common objects which constitute the page can be stored in the cache 16 and retrieved from the cache 16 by the Internet service provider 12 when requested by one of the users 14A-14N. Because it is faster for the Internet service provider 12 to retrieve the files from the cache 16 than through the Internet 10 from the content servers 8, the waiting time perceived by the user is decreased.
Several factors must be determined when designing an efficient cache system. For example, because the cache 16 has a finite memory storage capacity, the Internet service provider 12 must determine which HTML objects are most likely to be requested by the users 14A-14N. Therefore, usage pattern algorithms have been developed which determine which HTML objects should be stored in the cache 16 based upon the usage pattern of the users 14A-14N. In addition, the information in the cache 16 must be updated at regular time intervals. For example, a web page which provides stock quotes at approximately real time must be updated every several seconds. An advertising banner, such as might be shown on the YAHOO!® homepage, may be updated every hour. Other information on the YAHOO!® homepage, such as the morning headlines, may be updated once or twice a day. Other objects, such as the YAHOO!® logo, may remain valid for much longer periods of time. The usage pattern algorithm must also determine which HTML objects are worthy of caching and which are updated with such frequency as to be unworthy. In addition, the usage pattern algorithm can be used to determine when a HTML object stored in the cache 16 should be deleted and retrieved once again from the Internet 10 in order to update the file.
Based upon these factors, using an efficient usage pattern algorithm, as well as a manageable sized cache, it is reasonable to expect that approximately 60% of the data requested by the users 14A-14N can be stored within the cache 16. Even if the storage capacity of the cache 16 is greatly increased, it is difficult to achieve a caching rate at greater than 60% based upon modern Internet usage patterns.
The Internet service provider 12 can be coupled to the users 14A-14N using a variety of well-known techniques. For example, a copper line such as a standard, directly coupled plain old telephone service (POTS) can be used to connect the Internet service provider 12 to the remote unit 14A. Also cable modems and other digital subscriber lines (DSL) have been developed in order to increase the data rate of the connection between the Internet service provider and the user.
Using modern wireless communication techniques, the Internet service provider 12 can be coupled to one or more of the users 14A-14N using a wireless link rather than a wired line link. Typically, the finite capacity of the wireless link as well as the limited transmission rate of the wireless link can cause additional delays in the transmission of data between the Internet service provider and the user. In such a system, the benefits of reducing latencies in other areas of the system becomes more pronounced as cumulative delays increase the response time perceived by the users.
FIG. 2 is a block diagram of a prior art digital data system providing Internet connection over a wireless link. In FIG. 2, the system is configured as a terrestrial, system. A series of radio base stations 20A-20N are distributed throughout a geographic area where wireless Internet access is provided by the internet service provider 12. Each radio base station 20A-20N provides wireless communications to and from remote users within a corresponding physical coverage area. For example, in FIG. 2, users 14A-14N are shown to be within the coverage area of the base station 20A. Thus, when a remote unit requests digital data, such as a web page, a request for the web page is passed from the user 14 to the associated base station 20A. The base station 20A passes the request to the Internet service provider 12 incurring yet additional delays. The Internet service provider 12 provides the requested information from the cache 16 or through the Internet cloud 10 from the content servers 8A-8N, if the HTML objects are not available within the cache 16. The reverse process carries the objects back to the user, incurring yet additional delays. As noted above, the cumulative delay associated with transmission of the request over the wireless link as well as the other delays associated with response to the request can become intolerably high to the end-user.
Therefore, there has been a long felt need in the art to provide a means and method for providing efficient digital data access in a wireless communication system.